As we approached Krakatau by boat, it was hard to believe that this was the site of the catastrophic eruption in 1883 that killed around 35,000 people. All of the islands were very much alive: green and forested, containing all manner of wildlife (Figure 1). The birds were singing and giant lizards were prowling the beaches. When I say “all of the islands” there are four: Panjang, Sertung, Rakata and Anak Krakatau or “Child of Krakatau” (Figure 2). Both Panjang and Sertung are relic islands left behind after an eruption long before that of 1883. Rakata is the remnant of the 1883 edifice, left after the vast majority of the original volcanic island collapsed into the ocean as a result of the main explosions. Anak Krakatau is the newest of the four, the current active volcanic centre that emerged from the sea surface 44 years after the famous 1883 eruption. Anak is one of the fastest growing natural structures on earth at ~8 cm per week. Even at this distance, we could see the gases emanating from the top, reminding us that the tranquillity of these tropical islands could be disturbed at any given moment.

Figure 1a: The lusciously vegetated island of Rakata and b: the giant monitor lizards dwelling there.Figure 2: A map showing Krakatau’s volcanic islands, with the outline showing what they looked like prior to 1883. This map also shows Perboewatan and Danan, the two volcanic centres other than Rakata that were active in 1883, but were subsequently destroyed (Modified after Wiki user ChrisDHDR).

Yes, I am a volcanologist that, up until this moment, had never visited an active volcano. How did I even know I would like studying them? Well, I very much enjoy studying the products of volcanos: lavas and tephra. Tephra is any material ejected from a volcano during an explosive eruption, in contrast to effusive lavas. This may include ash or deposits left behind by destructive pyroclastic flows. However, I can tell you now that there is nothing quite as exciting as seeing the volcano you are studying in the flesh (Figure 3). This is why we do what we do, after all: to contribute to the knowledge on a volcano and volcanism as a whole in order to help those trying to monitor them. Monitoring active volcanoes is paramount when trying to save lives.

Figure 3: Anak Krakatau at sunset with visible gas emanating from the top.

Our first stop was Rakata. Reaching the cliffs we needed to sample wasn’t an easy task: we had to clamber over boulders with an approaching tide. The cliffs consisted of around 60 m of deposits from the 1883 eruption (Figure 4). It was hard to envisage all of that material being ejected and deposited in the space of just two days. There was also a lot of evidence for eruptions before that in 1883. We camped on Rakata for the night amongst the huge lizards and crabs. Dinner was served by the fantastic crew guiding us, and consisted of freshly caught fish. Sleeping in 26 degree heat didn’t particularly add to the experience though! The next day we visited Sertung where a little swimming was necessary to reach locations the boat simply couldn’t get to.

Panjang and Anak Krakatau were visited on our third day. The visit to Anak was particularly interesting. We saw evidence for the formation of this island as it emerged from the sea surface. Small concentric spheres or accretionary lapilli were observed in the deposits closest to the beach, and these form when an eruption comes into contact with water. Looking at these rocks really allowed us to imagine this island rising out of the ocean. As we climbed further up, we had to navigate our way through a field of volcanic bombs, erupted in 2012. Volcanic bombs are lumps of lava thrown out of a volcano as a projectile. Some of these were huge and left massive indentations or “bomb sags” in the ground when they landed. We walked across the most recent lava flow, which only formed 6 months ago (Figure 5). This reminds you how active this volcano really is. You have to be very careful when walking over old lava flows as they can have rubbly tops like these ones; it’s very easy to lose your footing and the rocks are very sharp.

Figure 5: Indiamber Jones and the Last Lava Flow.

When we woke up on the fourth day it was time to travel back to Carita, the port in Java we had travelled from. As we sailed away from Anak Krakatau the scale of the 100 m deep depression in the seafloor that was left by the 1883 eruption really hit me (Figure 6). The water between Rakata and Anak would have originally been island before it collapsed into a caldera during the 1883 eruption. This caldera collapse is likely responsible for the giant tsunami waves that claimed most of the lives in this catastrophe. After reading all about the history of the eruption, the eye-witness accounts and the scientific literature, being able to visit the island myself to collect samples really put all of this into context. The sense of awe was a rather poignant theme that ran through the core of our trip to the site of one of the most famous volcanic eruptions in the world.

Figure 6: The view of Rakata from Anak Krakatau at sunset on day 3. Prior to 1883 the water seen in the photo would have been island, and now represents the 100 m depression or caldera left behind in the sea floor after the land collapsed during 1883.